Recently, various digital audio coding techniques have been developed, and an increasing number of products regarding digital audio coding have been commercialized. Also, various multi-channel audio coding techniques based on psychoacoustic models have been developed and are currently being standardized.
Psychoacoustic models are established based on how humans perceive sounds, for example, based on the facts that a weaker sound becomes inaudible in the presence of a louder sound and that the human ear can nominally hear sounds in the range of 20-20,000 Hz. By using such psychoacoustic models, it is possible to effectively reduce the amount of data by removing unnecessary audio signals during the coding of the data.
Conventionally, a bitstream of a multi-channel audio signal is generated by performing fixed quantization that simply involves the use of a single quantization table on data to be encoded. As a result, the bitrate increases.